<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <title>Document</title>
  <style>
    body {
      margin: 0;
      padding: 0;
      background-color: #ddd;
    }
    div {
      width: 400px;
      height: 250px;
      margin: 20px 100px;
      background-color: #fff;
      background-image: radial-gradient(circle, #f00 20%, #fff 20%);
    }
  </style>
</head>
<body>
  <div></div>
</body>
</html>